The present invention relates generally to high-definition television (HDTV) systems. More specifically, the present invention relates to a method and apparatus for introducing a pan and scan feature in the compatible channel of a multiple-signal HDTV system.
In a typical multiple signal HDTV system with two channels, an HDTV signal, which requires a larger bandwidth than is available on a standard television (TV) channel, is converted into two signals--one of them compatible with a standard TV receiver, such as an NTSC receiver--to be broadcast in separate channels. An HDTV receiver then combines the two signals to form an HDTV picture having, for example, a wider aspect ratio (width of the picture divided by its height) and greater resolution than for a standard picture. One prior art scheme for broadcasting such signals divides the HDTV signal into a center portion to be broadcast in the compatible channel, and information representing panels contiguous to the center portions along with other augmenting information in the second (augmentation) channel.
Because the HDTV picture is wider than that of a standard TV signal, it is desirable to introduce a pan and scan feature to the compatible channel so as to selectively focus the picture received by a standard receiver on different portions (horizontal) of the HDTV picture; i.e., pan and scan. For example, important details in an HDTV picture may appear at the the leftmost edges of the picture. Without a pan and scan feature, the standard receiver will always receive only the same fixed portion of HDTV picture to the exclusion of information at the edges of the HDTV picture.
Introducing a pan and scan feature involves additional complexity to an HDTV system since the portion broadcast in the compatible channel is variable with respect to its position within the HDTV picture, thus making the panels and other augmenting information variable in their relative dimensions.